SPEE curve is a straight line connecting the incisor edge of mandibular incisor, the cusp of canine, the buccal tip of premolar and the mesial and distal buccal tip of molar, and it is a concave curve from front to back.

Complete teeth need two curves to maintain and balance, SPEE curve and Wilson curve.

In orthodontics, there is a reference standard of SPEE among the related factors about whether tooth extraction is needed:

The height of Spee curve is the vertical distance between the buccal cusp of the second bicuspid tooth and the plane formed by the lower anterior tooth and the buccal sulcus of the second permanent molar measured on the mandibular arch model. Every time the 1mm Spee curve is leveled, the dental arch gap of 1mm is needed.

Other details are as follows:

In contemporary orthodontic practice, the objective factors that determine whether a specific patient needs tooth extraction can be summarized into the following seven aspects:

1. Tooth crowdedness: The clearance of 1 mm is needed to relieve the crowdedness of 1 mm, and whether or not to extract the tooth and the location of the tooth will be decided after the clearance analysis.

2.Spee curve height: Every time a Spee curve of 1mm is leveled, an arch gap of 1mm is required.

3. Protrusion of dental arch: the gap needed to make the protruding incisors stand back to the normal position.

4. Bone surface type: the position of incisors and the sagittal and vertical position between the upper and lower jaws are of great value in deciding whether to extract teeth. Under the condition of the same factors such as tooth crowding and dental arch protrusion, the extraction standard of patients with high angle can be relaxed, and patients with low angle should be strictly controlled. The purpose of tooth extraction is not only to align the dentition, but also to compensate for the disharmony between the upper and lower jaws by moving the front teeth within a certain range.

5. Use anchorage to estimate molar movement.

6. Soft tissue profile: the analysis of labial process reflecting the relationship between nose, lips and chin can not be ignored.

7. Growth and development factors: determine the growth and development stage of the patient, determine the treatment method, predict the possible growth changes of the patient during the treatment, and predict the growth impact of treatment on adolescence.